In a heterogeneous wireless cellular communication network, Het net, low power nodes, LPN, such as pico base stations, may be mixed with high power nodes, HPN, such as macro base stations. A LPN transmits downlink, DL, signals with a lower power than a HPN. A LPN output power may for example in an in-building solution be in the range of 100 mW whereas an output power of a HPN may be in the range of 5 W to 60 W.
The coverage of a LPN may be limited by a neighboring HPN. A UE is usually instructed to select serving base station based on received signal strength. If the signal strength of a signal received from a HPN is higher than the signal strength of a signal received from a LPN, the HPN is selected as the serving base station for the UE. However, the HPN may not be the best choice for the UE in terms of uplink, UL, signal strength. In other words, the UE has to send UL signals with higher signal strength to a HPN than to a LPN that is situated closer to the UE. Thereby, more power is consumed for the UE, if it communicates with the HPN than the LPN. For this reason, and also for network resource utilization purposes, cell range expansion, CRE, may be used in the network. For CRE, a handover bias can be added in favor of the LPN, meaning that for selecting the HPN as serving base station, the received signal strength from the HPN has to be more than the received signal strength from the LPN plus a bias value. Consequently, the coverage of the LPN is increased without increasing the output power of the LPN.
However, UEs that are situated in a CRE area and that communicate with the LPN will experience strong DL interference from the HPN. For this reason, interference management schemes are needed between the HPN and the LPN such that the HPN has a transmission interrupt or transmits Almost Blank Subframes, ABS, in a transmission time interval, TTI, when the LPN is scheduled to transmit to the UE residing in a CRE area. ABS is standardized in 3GPP for LTE. In other words, ABS is used at the HPN when the LPN is transmitting, such that at the UE the signals from the HPN are not interfering with the signals from the LPN. This means that network resources from a HPN are temporarily not utilized during a TTI (or a subframe), network resources that could otherwise have been used for e.g. supporting UEs residing in the coverage area of the HPN. Consequently, there is an interest in a wireless communication network to balance the advantages of connecting UEs situated in a CRE area of a LPN to the LPN with the drawbacks of having a HPN reducing the transmitting activity during the subframes when the LPN transmits to such a UE.